The present invention generally relates to a bar-code reading apparatus, and particularly relates to an improvement for efficiently performing bar-code reading.
There are several types of conventionally used bar-code reading apparatuses. Namely, there are (i) the pen type in which an operator holds a pen-like casing provided with a reading head at its front end so as to manually scan a bar-code from its one end to its other end by using the reading head; (ii) the touch type in which the apparatus makes contact with a bar-code and in which a symbol surface on which the bar-code is formed, is illuminated so that reflective light from the symbol surface is directed towards a linear image sensor so as to form a bar-code image on a photo detection surface of the linear image sensor; (iii) the laser type in which a bar-code is scanned at a high speed by a laser spot so that reflective light from the symbol surface is detected to thereby perform the reading;
In view of the mode of use, the above reading apparatuses are classified into that of the holding type in which an operator performs reading while holding the reading apparatus and that of the fixed type in which the reading apparatus is disposed in the fixed state and a symbol surface on which a bar-code is formed is directed to the apparatus.
In all the foregoing bar-code reading apparatuses except the pen-type bar-code reading apparatus in which a bar-code scanning is performed manually, reading is made by plural times of bar-code scanning. That is, a bar-code is scanned by a laser spot by plural times in the laser-type bar-code reading apparatus, and a bar-code image formed on a photo detection surface of an image sensor is electrically scanned by plural times in the touch-type bar-code reading apparatus.
Further, since the scanning by means of a laser spot is continuous, the electric scanning is performed before a bar-code enters the range of the reading field of view of the apparatus and there occurs inevitably a state where a scanning line SL crosses only a part of a bar-code 1 as shown in FIGS. 3A and 3B in the process in which the reading apparatus is brought toward the bar-code or the bar-code is directed to the reading apparatus. In order to correctly read the bar-code 1, it is necessary to establish the positional relation between the reading apparatus and the bar-code 1 so that the scanning line SL crosses the whole of the bar-code 1 from its one end to its other end as shown in FIG. 3C. Therefore, correct reading cannot be expected in the respective states illustrated in FIGS. 3A and 3B, and consequently there is a possibility of occurrence of erroneous reading in the process in which the positional relation between the bar-code and the reading apparatus is being established.
A bar-code expresses one digit (or one English character), for example, by a plurality of bars and spaces which are of different thicknesses from one another. However, generally, the number of digits or characters in whole of the bar-code is not fixed. Therefore, even when the scanning line SL crosses only a part of the bar-code 1 as shown in FIGS. 3A and 3B, if scanning is performed to the boundary of digits, decoding is performed to that position and the result of the partial decoding is erroneously recognized as the result of the whole decoding, so that erroneous data are supplied to a computer or the like.
In order to correctly perform a processing in a computer, for example, a check digit (a kind of parity) is sometimes added to a bar-code in advance so that when the number of digits are not equalized, it is determined that there is a reading error and a signal for instructing another reading is applied to the reading apparatus. In such cases, however, it takes a long time until the instruction to make another reading is applied from the computer to the reading apparatus. Therefore, it is necessary for the operator to perform the procedure for reading the bar-code again. As a result, the efficiency of data input work for bar-code reading is remarkably lowered.